The objective of the project was to investigate the effects of whole body irradiation of the mouse on the number of sister chromatid exchanges in bone marrow cells. The measurement of sister chromatid exchange (SCE) constitutes the most sensitive indicator yet developed for detecting cytogenetic effects of mutagens and carcinogens. We utilized this sensitive assay to investigate potential mutagenic bioeffects of 2450 MHz CW microwave radiation by comparing the incidence of SCE in bone marrow cells of 12 exposed mice, 12 sham controls, and 12 standard controls. The animals were exposed from above for 8 hours/day to an incident power density of 20 mW/cm2 (SAR determined to be 15.4 mW/gm). The exposure was for 28 days. Immediately after termination of exposure, the animals were prepared for analysis. Results after scoring more than 300 cells show that the incidence of SCE's in the exposed group is not significantly different from the unexposed controls. The value is approximately 3.0 exchanges per cell.